DESCRIPTION: The long term goal of this application is to understand the mechanisms involved in apoptosis in prostate cancer. Apoptosis is an attractive therapeutic target for prostate cancer because it is a slow growing malignancy and resistant to most therapeutic agents. The study is focused on Fas, which plays a fundamental role in apoptosis in lymphoid cells. In preliminary studies, the investigators have identified Fas expression in human prostate cancer cell lines, some of which can undergo Fas-mediated apoptosis. It is also found that human prostate cells, both benign and malignant, express Fas, as determined by immunohistochemical staining of frozen tissue sections. They also find that Fas ligation of prostate cell lines induced rapid tyrosine phosphorylation/dephosphorylation of multiple proteins and that treatment with cycloheximide can convert the phenotype of some Fas-resistant prostate cancer cell lines to the Fas-sensitive state. Based on these findings, they hypothesize that Fas-mediated signal transduction mechanisms and the relevant components of the apoptotic machinery are generally intact in both sensitive and resistant cells, and that suppression of Fas-mediated apoptosis in resistant cells is controlled by cellular regulatory factors. To understand the differences between the resistant and sensitive prostate cancer cell lines and to identify the mechanisms which are responsible for resistance to Fas-mediated apoptosis, they propose to (1) determine the role of a ceramide-dependent mechanism in Fas-mediated apoptosis, (2) determine the role of Bcl-2 family proteins in Fas-mediated apoptosis, (3) determine the role of CD40 and NF-kappaB on TNF-alpha and Fas-mediated apoptosis, and (4) isolate genes encoding factors responsible for resistance to Fas-mediated apoptosis.